(a) Field of the Invention
The present invention relates to a method and apparatus for transmitting and receiving an OFDM signal in an orthogonal frequency division multiplexing (OFDM) system.
(b) Description of the Related Art
OFDM is 4G modulation technology that is expected to be selected as a digital TV standard of Europe, Japan, and Australia. OFDM technology is a kind of a multicarrier modulation method, and distributes and transmits data to a plurality of carriers that are separated by a predetermined gap. An OFDM system exhibits excellent performance in a multi-path and mobile reception environment through such a modulation transmission method.
However, when a signal that is formed with a plurality of subcarriers is added with the same phase in a time domain, in OFDM that is multiplexed with a plurality of carriers, a peak to average power ratio (PAPR) increases. When the PAPR increases, a power amplifier operates in a saturation area rather than a linear operation area, and thus a signal may be distorted. In order to prevent this, an excessive dynamic range should be set to a power amplifier, and this deteriorates efficiency of the power amplifier.
In order to solve the above problem, a constant envelope (CE) OFDM transmission method of a form in which an analog method (FM/PM) is coupled may be used. A CE-OFDM system has a characteristic that in a baseband, a PAPR is 0, and an amplitude of a transmitting signal is the same in a time axis.
In a CE-OFDM system, because a signal that is output after inverse discrete Fourier transform (IDFT) generally represents a Gaussian distribution of average 0, the signal is largely affected by noise.